1. Field of the Invention
This invention relates to an upward deflecting metal support disk useful in a seal for an electrochemical cell. More particularly, this invention relates to an electrochemical cell, such as a primary alkaline cell, sealed at one end with a seal containing a support disk which exhibits a resilient outward radial force against the seal and deflects slightly upward when radially compressed during the sealing process, to assure seal integrity and a positive electrical contact with the metal end cap terminal of the cell.
2. Background of the Disclosure
Electrochemical cells, such as alkaline primary cells, are made by filling a metal can open at one end and closed at the other end, with the electrochemically active ingredients, inserting a seal assembly in the open end and then crimping to seal the cell. The seal assembly includes a disk of plastic or metal as a support against which the seal is made to prevent leakage of the cell's internal chemical components. Therefore, the support disk must be strong enough to make a seal without being crushed during the sealing step of the manufacturing process. Seals employing a rigid metal disk do not contract and expand through temperature variations in a manner which maintains an even pressure on the seal. This is due to the differences in the thermal expansion and contraction characteristics of the metal can, the different materials employed in the seal, including the metal support disk, manufacturing tolerance variables which can not be avoided and creep of the plastic seal member. As a result, such cells are prone to leakage. Similarly, if the support is thick plastic, the large seal area results in a lower pressure exerted on the seal. An example of such a fairly rigid type of plastic support is disclosed, for example, in U.S. Pat. No. 5,227,261. More recently, there have been efforts to develop a more resilient seal for an electrochemical cell. These efforts have resulted in the development of a seal assembly which includes an electrically nonconductive, plastic seal member, a metal support disk, a current collector and a metal end cover or cap which serves as one terminal of the cell. The metal support disk permits the cell to be sealed by a crimping step which exerts radially inward forces to the seal assembly and which radially compresses the support to a small extent. The member which achieves the actual seal is generally disk or wheel-shaped and is fabricated as a single piece of injection molded plastic, although some assemblies have employed two or more plastic members to achieve the seal. Illustrative, but non-limiting examples of seal assemblies employing a plastic seal member, metal support disk, current collector and metal end cap terminal and their use with electrochemical cells are disclosed, for example, in U.S. Pat. Nos. 4,537,841 and 5,080,985. However, there is still a need for a seal having a support disk which will maintain a fairly uniform and constant pressure on the seal over the anticipated temperature range through which the cell may be in service, in order to maintain seal integrity and at the same time insure that electrical contact with the end cap terminal is maintained.